A cranial computed tomography, also known as a head CT or CAT scan, is a noninvasive process by which medical professionals can examine the inside of the skull and brain. The patient is placed into an electronic scanning machine, which scans the head from several angles and generates images for the doctor. As CTs use both x-ray beams and electronic x-ray detectors to collect images, they provide more detail than regular x-rays. The results of a head CT are typically used to detect, evaluate, and research trauma, illness, or changes in the head and brain.
Before a head CT, the patient is usually given a gown to wear. Patients are also instructed to remove all items that could interfere with the results, such as glasses, hair pins, jewelry, and even dentures. In some cases, the patient is also asked to abstain from eating or drinking for a set period of time before the procedure.
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During the head CT, the patient lies still on a table, usually flat, but occasionally positioned on the side or stomach. The table is then wheeled inside a large, box-shaped scanning machine with a tunnel in the center. Once the patient is in place, x-ray and electronic detectors move around the patient’s head, taking a cross-section of data from opposite positions on a ring called a gantry. When the scan is complete, the data is translated into images, which are delivered to a computer in an adjoining room. These images can be viewed on the monitor, printed out, or saved on a data storage device.
A head CT usually takes several minutes to complete. It is painless, though some patients may find it unpleasant trying to lie still in such close surroundings. Some patients who feel stress or discomfort during or before the process may be offered a mild sedative.
The most common reasons for performing a head CT include brain tumors and infections, bleeding in the brain, and abnormal development of the neck or head. A head CT may also be used to help a doctor to determine what is causing conditions such as headaches, hearing loss, muscle weakness, or vision problems. The process can help medical professionals to define a new stroke, evaluate injuries, or research behavioral changes.
Some conditions may increase the risk of having a head CT and should be disclosed to both the doctor and the radiologist performing the scan. These include asthma, kidney disease, diabetes, thyroid problems, or heart disease. Pregnant women or women who think they are pregnant are typically advised not to have a head CT due to the risk of birth defects.